U.S. patent application number 15/827291 was filed with the patent office on 2019-05-30 for single-sided four-way indexable positive cutting insert and insert mill therefor.
The applicant listed for this patent is Iscar, Ltd.. Invention is credited to ASSAF BALLAS.
Application Number | 20190160563 15/827291 |
Document ID | / |
Family ID | 66634758 |
Filed Date | 2019-05-30 |
United States Patent
Application |
20190160563 |
Kind Code |
A1 |
BALLAS; ASSAF |
May 30, 2019 |
SINGLE-SIDED FOUR-WAY INDEXABLE POSITIVE CUTTING INSERT AND INSERT
MILL THEREFOR
Abstract
A single-sided four-way indexable cutting insert includes a
positive basic shape, a rake surface, a peripheral surface
including four side abutment surfaces, a base bearing surface and a
screw hole connecting the rake and base bearing surfaces. The
insert has an imaginary square frustum which defines a square base
containing the cutting insert's base bearing surface, and further
defines four isosceles trapezoid side surfaces respectively
containing the cutting insert's four side abutment surfaces. A
material volume V.sub.F of the cutting insert and a void volume
V.sub.S of the insert fulfill the condition
V.sub.S/V.sub.F.gtoreq.0.25.
Inventors: |
BALLAS; ASSAF; (Akko,
IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Iscar, Ltd. |
Tefen |
|
IL |
|
|
Family ID: |
66634758 |
Appl. No.: |
15/827291 |
Filed: |
November 30, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23C 2200/045 20130101;
B23C 2200/085 20130101; B23C 2210/0407 20130101; B23C 2200/125
20130101; B23C 2200/0455 20130101; B23C 5/06 20130101; B23C
2210/0442 20130101; B23C 5/207 20130101; B23C 5/109 20130101; B23C
5/241 20130101 |
International
Class: |
B23C 5/20 20060101
B23C005/20; B23C 5/24 20060101 B23C005/24; B23C 5/06 20060101
B23C005/06 |
Claims
1. A single-sided, four-way indexable cutting insert having a
positive basic shape and comprising: a rake surface; a base bearing
surface located opposite the rake surface; an insert axis A.sub.I
extending perpendicular to the base bearing surface and through the
center of the insert, the insert axis defining: an upward direction
from the base bearing surface towards the rake surface, a downward
direction opposite to the upward direction, and an outward
direction perpendicular to the upward and downward directions and
extending away from the insert axis; a cutting insert height
H.sub.I measurable parallel to the insert axis, from the base
bearing surface to a highest point of the rake surface; a
peripheral surface connecting the rake surface and base bearing
surface, the peripheral surface comprising: an unground lower
sub-surface which extends upwardly and outwardly from the base
bearing surface, the lower sub-surface comprising first, second,
third and fourth side abutment surfaces; and an upper sub-surface
connecting the lower sub-surface and the rake surface, the upper
sub-surface beginning in the upward direction at a minimum upper
surface height H.sub.U above the base bearing surface; a cutting
edge formed along an intersection of the peripheral surface and
rake surface; a screw hole opening out to the rake and base bearing
surfaces, the screw hole having a void volume V.sub.S; wherein: the
insert has an imaginary square frustum defined by: a square base
containing the base bearing surface; four isosceles trapezoid side
surfaces, each extending upwardly and outwardly from the square
base at an abutment surface relief angle .theta. fulfilling the
condition 1.degree..ltoreq..theta..ltoreq.15.degree., and each
containing a respective one of the first, second, third and fourth
side abutment surfaces; and a square top connecting the four
isosceles trapezoid side surfaces and located a distance equal to
the cutting insert height H.sub.I from the square base; the upper
sub-surface comprises at least one overhanging portion, which
extends outwardly from an adjacent one of the trapezoid side
surfaces and has a lowermost point at said minimum upper
sub-surface height H.sub.U; in a view parallel to the insert axis
A.sub.I, an inscribed circle diameter I.sub.C of the cutting edges
fulfills the condition I.sub.C.ltoreq.10 mm; and a volume ratio
V.sub.S/V.sub.F of the void volume V.sub.S and a material volume
V.sub.F of the cutting insert fulfills the condition
V.sub.S/V.sub.F.gtoreq.0.25.
2. The cutting insert according to claim 1, wherein the volume
ratio fulfills the condition: V.sub.S/V.sub.F.gtoreq.0.30.
3. The cutting insert according to claim 1, wherein the volume
ratio fulfills the condition: V.sub.S/V.sub.F.ltoreq.0.60.
4. The cutting insert according to claim 1, wherein the inscribed
circle diameter I.sub.C fulfills the condition: I.sub.C.ltoreq.8
mm.
5. The cutting insert according to claim 4, wherein the inscribed
circle diameter I.sub.C fulfills the condition: I.sub.C.ltoreq.6.5
mm.
6. The cutting insert according to claim 5, wherein the inscribed
circle diameter I.sub.C fulfills the condition: I.sub.C.ltoreq.5
mm.
7. The cutting insert according to claim 1, wherein the inscribed
circle diameter I.sub.C fulfills the condition: I.sub.C.gtoreq.3.5
mm.
8. The cutting insert according to claim 1, wherein the minimum
upper sub-surface height H.sub.U fulfills the condition:
0.60H.sub.I.ltoreq.H.sub.U.ltoreq.0.90H.sub.I.
9. The cutting insert according to claim 8, wherein the minimum
upper sub-surface height H.sub.U fulfills the condition:
0.63H.sub.I.ltoreq.H.sub.U.ltoreq.0.73H.sub.I.
10. The cutting insert according to claim 1, wherein the at least
one overhanging portion is a plurality of overhanging portions.
11. The cutting insert according to claim 1, wherein the cutting
edge comprises four identical corners and four identical straight
edges connecting the corners.
12. The cutting insert according to claim 11, wherein each straight
edge has an edge length L.sub.E which fulfills the condition:
0.65I.sub.C<L.sub.E<0.95l.sub.C.
13. The cutting insert according to claim 12, wherein each straight
edge has an edge length L.sub.E which fulfills the condition:
0.75I.sub.C<L.sub.E<0.90l.sub.C.
14. The cutting insert according to claim 1, wherein only the base
bearing surface of the cutting insert is ground.
15. The cutting insert according to claim 14, wherein the cutting
edge is contained within the square top.
16. The cutting insert according to claim 1, wherein the base
bearing surface and the entire cutting edge are ground and the
cutting edge is contained within the square top.
17. The cutting insert according to claim 1, wherein the cutting
edge is circular.
18. The cutting insert according to claim 1, wherein the abutment
surface relief angle .theta. fulfills the condition
4.degree..ltoreq..theta..ltoreq.7.degree..
19. An insert mill comprising: a tool holder; and a cutting insert
according to claim 1 seated in the tool holder; the tool holder
comprising: a shank portion; a cutting portion connected to the
shank portion and comprising a pocket; and a rotation axis
extending through the center of the tool holder and defining a
forward direction extending from the shank portion in the direction
of the cutting portion; the pocket comprises: a seat abutment
surface; a threaded pocket hole opening out to the seat abutment
surface and defining a minimal pocket hole inscribed circle I.sub.P
and an associated minimal pocket hole diameter D.sub.P; and first
and second lateral abutment surfaces oriented at a right angle to
each other in a plan view of the seat abutment surface; each of the
first and second lateral abutment surfaces has an elongated
continuous shape, the first and second lateral abutment surfaces
being the only abutment surfaces of the pocket apart from the seat
abutment surface; and the cutting insert is mounted to the pocket
with the insert's base bearing surface abutting the pocket's seat
abutment surface, and two of the insert's adjacent side abutment
surfaces abutting the pocket's first and second lateral abutment
surfaces.
20. The insert mill according to claim 19, wherein: the cutting
edge is circular; and the insert's two adjacent side abutment
surfaces abut center portions of the pocket's first and second
lateral abutment surfaces.
Description
FIELD OF THE INVENTION
[0001] The subject matter of the present invention relates to
single-sided four-way indexable positive cutting inserts
(hereinafter also "insert(s)") and insert mills therefor. More
particularly, to relatively small such inserts and tool holders
configured for 90.degree. shoulder milling operations.
BACKGROUND OF THE INVENTION
[0002] For the purposes of the present invention, end mills can be
theoretically divided into two general groups, namely insert-mills
and solid end mills.
[0003] Insert-mills are milling tools which comprise tool holders
with pockets and replaceable inserts, typically indexable,
configured to be mounted in the pockets. An advantage of
insert-mills is that the replaceable inserts, which are made of
comparatively expensive, harder, material constitutes a relatively
small portion of the milling tool. The tool holders comprise a
shank which is held securely by a collet or chuck during
milling.
[0004] Unlike insert-mills which regularly require replacement of
small inserts and less regularly require replacement of the tool
holder, solid end mills comprise integrally formed teeth and the
entire solid end mill is replaced after it is worn. Solid end mills
also comprise an integrally formed shank which is held securely by
a collet or chuck during milling. Accordingly, solid end mills
utilize far more comparatively expensive material than
insert-mills. Despite the comparatively higher cost, one of the
advantages of solid end mills over insert-mills is that the solid
end mill's single integrally formed body can be manufactured with a
comparatively smaller diameter (typically less than 20 mm diameter,
with smaller diameters being more popular, e.g., at about 12 mm
diameter) allowing milling in relatively smaller locations than is
possible or practical with insert-mills.
[0005] While very small inserts are known, solid end mills are
still commonly preferred at the relatively smaller diameters for a
variety of reasons.
[0006] Accordingly, the present invention is directed to inserts
and insert mills that have a range of design features that make
them functionally and economically competitive with solid end mills
at cutting diameters of 20 mm and less, particularly in the range
of 9 to 16 mm, preferably 9 to 12 mm.
[0007] A publication of interest is EP 3050655, which discloses
single-sided two-way indexable inserts for small diameter tool
holders.
SUMMARY OF THE INVENTION
[0008] The present invention provides a single-sided four-way
indexable cutting insert for 90.degree. shoulder milling operations
for small diameter tool holders. Four indexable positions are
typically preferred over the two indexable positions disclosed in
EP 3050655, yet the design chosen in EP 3050655 was deliberately
chosen to have only two indexable positions, presumably because
this was the optimal design conceived by the inventors thereof for
small diameter tool holders.
[0009] The present invention conceives that even at such small
diameters a four-way indexable insert, e.g. of basic square shape,
can be provided. Traditionally, during 90.degree. shoulder milling
operations for four-way indexable inserts, two adjacent cutting
edges of the insert will be used simultaneously, one radially
located cutting edge for machining laterally and another axially
located cutting for providing a wiper function at the axial end of
the insert mill. Since the cutting edge providing the wiper
function already undergoes wear, it was believed that four
indexable positions were not available, and such inserts were
disadvantageous over the elongated two-way indexable type shown in
EP 3050655, which can provide a longer cutting edge.
[0010] It will be noted that cutting inserts having more than four
cutting edges on one side are known, however these inserts are not
known for such small diameters. This is because, in order to
compensate for the above-mentioned wear on a cutting edge used as a
wiper, the cutting edge is typically not straight but comprises a
small wiper portion and a larger relieved cutting edge portion.
Thus the overall cutting edge length of an already small insert is
reduced.
[0011] Similarly, double sided inserts with even more than four
edges are known, but being able to provide clearance for such
cutting inserts in extremely small diameter tool holders is
problematic.
[0012] Accordingly, it has been found by the present inventor that
the wiper function has not caused significant wear and a usage of
the entire cutting edge, even after it has been used in a wiper
position, as a main cutting edge position is possible for small
diameter tool holders.
[0013] Additionally, a number of advantageous features have been
incorporated, each of which is designed to allow economical
production in order for an insert mill of small diameter to be
competitive against solid end mills of similar diameter, as will be
described below.
[0014] According to a first aspect of the present invention there
is provided a single-sided, four-way indexable cutting insert
having a positive basic shape and comprising: a rake surface; a
base bearing surface located opposite the rake surface; an insert
axis (A.sub.I) extending perpendicular to the base bearing surface
and through the center of the insert, the insert axis defining: an
upward direction from the base bearing surface towards the rake
surface, a downward direction opposite to the upward direction, and
an outward direction perpendicular to the upward and downward
directions and extending away from the insert axis; a cutting
insert height H.sub.I measurable parallel to the insert axis, from
the base bearing surface to a highest point of the rake surface; a
peripheral surface connecting the rake surface and base bearing
surface, the peripheral surface comprising: an unground lower
sub-surface which extends upwardly and outwardly from the base
bearing surface, the lower sub-surface comprising first, second,
third and fourth side abutment surfaces; and an upper sub-surface
connecting the lower sub-surface and the rake surface, the upper
sub-surface beginning in the upward direction at a minimum upper
surface height H.sub.U above the base bearing surface; a cutting
edge formed along an intersection of the peripheral surface and
rake surface; a screw hole opening out to the rake and base bearing
surfaces, the screw hole having a void volume V.sub.S; wherein: the
insert has an imaginary square frustum defined by: a square base
containing the base bearing surface; four isosceles trapezoid side
surfaces, each extending upwardly and outwardly from the square
base at an abutment surface relief angle .theta. fulfilling the
condition 1.degree..ltoreq..theta..ltoreq.15.degree., and each
containing a respective one of the first, second, third and fourth
side abutment surfaces; and a square top connecting the four
isosceles trapezoid side surfaces and located a distance equal to
the cutting insert height H.sub.I from the square base; the upper
sub-surface comprises at least one overhanging portion, which
extends outwardly from an adjacent one of the trapezoid side
surfaces and has a lowermost point at said minimum upper
sub-surface height H.sub.U; in a view parallel to the insert axis
(A.sub.I), an inscribed circle diameter I.sub.C of the cutting
edges fulfills the condition I.sub.C.ltoreq.10 mm; and a volume
ratio V.sub.S/V.sub.F of the void volume V.sub.S and a material
volume V.sub.F of the cutting insert fulfills the condition
V.sub.S/V.sub.F.gtoreq.0.25.
[0015] In addition to the above-mentioned discovery about the wiper
surface, by utilizing a small insert, namely having an inscribed
circle diameter I.sub.C of less than or equal to 10 mm, it has been
found that such small inserts undergo relatively small distortion
(typically a convex bulge) in the sintering process. Such
distortion is traditionally dealt with by either providing a pocket
lateral abutment surface with a gap (to ensure the convex insert
side abutment surface securely contacts the lateral abutment
surface on both sides of the gap), or by providing a pre-designed
recess on the side surface of the cutting insert, or by expensive
grinding of the side of the cutting insert.
[0016] Since the cutting insert of the present invention is small,
the distortion is within reasonable tolerances and the
above-mentioned modification of the pocket and peripheral grinding
of the cutting insert can be avoided. Thus, the insert is defined
as having an unground lower sub-surface. As is known in the art,
ground surfaces can be identified by grinding lines and
discontinuity lines where a planar ground surface ends and an
unground surface starts.
[0017] Further, such pocket design is thereby also useful for small
four-way indexable circular-type inserts, which typically cannot be
mounted to the same pocket as they contact the center of the
lateral abutment surface (and hence would contact a gap in the
traditional lateral abutment surface). Further, other types of
inserts such as four-way indexable feed inserts could also be used
with such tool holders, making the tool holders of the present
invention more versatile and hence more economical.
[0018] Accordingly, there is an additional advantageous feature of
the at least one overhanging portion, which separates the
peripheral portion of the insert for mounting to the insert pocket
(i.e. the lower sub-surface) and the cutting portion of the insert
(i.e., the cutting edge). Thus, when producing different cutting
edge types (90.degree. or circular, etc.) the same basic insert, or
at least the same pocket, can be used.
[0019] Having a positive basic shape, i.e. allowing a pressing
process with as little machining as possible, as disclosed in EP
3050655B1 (par. [0034]), also contributes to the economic advantage
of the present design. It will be noted that the term "positive
basic shape" more specifically means that cross sectional areas
nearer to a base bearing surface of the insert are smaller than
cross sectional areas further away therefrom, but does not require
all the peripheral surfaces to be continuously slanted. For
example, at certain sections of the insert the surfaces may extend
parallel with an insert axis.
[0020] Finally, the amount of material of the insert itself can be
minimized. It has been found that the volume ratio V.sub.S/V.sub.F
defined above has performed successfully. Naturally, minimizing the
amount of material and providing four indexable positions can
provide an economic advantage.
[0021] While each of the four main design features mentioned above
(namely, four indexable positions, unground lower sub-surface due
to small size, at least one overhanging portion, and volume
minimizing material) are each individually advantageous the
combination of all four elements in the present aspect is believed
to provide a cutting insert with multiple advantages.
[0022] Additionally, while the intended use of the main insert of
the present invention is 90.degree. shoulder milling operations,
such inserts are extremely small and versatile and hence could be
used for other operations such as chamfering (by rotating a pocket
orientation) or drilling, etc.
[0023] According to a second aspect of the present invention there
is provided an insert mill comprising: [0024] a tool holder; and
[0025] a cutting insert according to the previous aspect.
[0026] In such an insert mill, the tool holder can comprise: [0027]
a shank portion; [0028] a cutting portion connected to the shank
portion and comprising a pocket; and [0029] a rotation axis
extending through the center of the tool holder and defining a
forward direction extending from the shank portion in the direction
of the cutting portion;
[0030] with the pocket comprising: [0031] a seat abutment surface;
[0032] a threaded pocket hole opening out to the seat abutment
surface and defining a minimal pocket hole inscribed circle I.sub.P
and an associated minimal pocket hole diameter D.sub.P; and [0033]
first and second lateral abutment surfaces oriented at a right
angle to each other in a plan view of the seat abutment
surface;
[0034] and wherein: [0035] each of the first and second lateral
abutment surfaces has an elongated continuous shape, the first and
second lateral abutment surfaces being the only abutment surfaces
of the pocket apart from the seat abutment surface; and [0036] the
cutting insert is mounted to the pocket with the insert's base
bearing surface abutting the pocket's seat abutment surface and two
of the insert's adjacent side abutment surfaces abutting the the
pocket's first and second lateral abutment surfaces.
[0037] It should be noted that the above defined "right angle" is
not meant to mean exactly 90.degree. but rather within
manufacturing tolerances, i.e. about 90.degree..+-.3.degree.,
preferably 90.degree..+-.1.degree..
[0038] As mentioned above, a four-way indexable insert with an
unground lower sub-surface and a pocket as defined above allows
simple production of the pocket and versatility in that the pocket
can also accommodate even other types of four-way indexable
inserts.
[0039] According to a third aspect of the present invention there
is provided a tool holder as defined in the second aspect.
[0040] According to a fourth aspect of the present invention there
is provided a four-way indexable cutting insert having a circular
cutting edge and exactly four equally spaced side abutment
surfaces.
[0041] According to a fifth aspect of the present invention there
is provided a four-way indexable cutting insert having a volume
ratio of V.sub.S/V.sub.F.gtoreq.0.30.
[0042] It will be understood that a greater volume ratio utilizes
less material. Accordingly it is preferred that the volume ratio
fulfills the condition: V.sub.S/V.sub.F.gtoreq.0.30, or even
V.sub.S/V.sub.F.gtoreq.0.35. An approximated maximum volume ratio
for acceptable modern cutting conditions is, theoretically,
believed to fulfill the condition: V.sub.S/V.sub.F.ltoreq.0.55.
This maximum volume ratio is particularly relevant to a
circular-type insert which has extremely little material according
to the present invention. With regard to square edged inserts, an
approximated maximum volume ratio of V.sub.S/V.sub.F.ltoreq.0.40 is
likely the approximate maximum volume ratio.
[0043] It will be understood that even though the inscribed circle
diameter I.sub.C defined above allows the lower sub-surface to be
unground, even smaller sizes will allow smaller diameter tool
holders to be used and/or to have additional inserts. Accordingly
it is preferred that the inscribed circle diameter I.sub.C fulfills
the condition: I.sub.C.ltoreq.8 mm, or even I.sub.C.ltoreq.6.5 mm,
and most preferably I.sub.C.ltoreq.5 mm. An approximated minimum
feasible size is believed to fulfill the condition:
I.sub.C.gtoreq.3.5 mm.
[0044] It will be understood that a larger minimum upper
sub-surface height H.sub.U allows a greater height of the lower
sub-surface. The lower sub-surface provides a bearing function and
hence a maximized height thereof provides greater stability to the
insert when mounted in the pocket. Conversely, sufficient size of
the upper sub-surface is needed for the cutting function.
Accordingly, it is preferred that the minimum upper sub-surface
height H.sub.U fulfills the condition:
0.60H.sub.I.ltoreq.H.sub.U.ltoreq.0.90H.sub.I, or even
0.60H.sub.I.ltoreq.H.sub.U.ltoreq.0.80H.sub.I, and most preferably
0.63H.sub.I.ltoreq.H.sub.U.ltoreq.0.73H.sub.I.
[0045] The at least one overhanging portion can be a single
continuous overhanging portion extending along the entire periphery
of the insert or can be a plurality of circumferentially spaced
apart overhanging portions, as is preferred in some embodiments,
such as the circular edge insert, as explained below.
[0046] The cutting insert can preferably be 90.degree. rotationally
symmetric about the insert axis. Stated differently, the cutting
insert can have four identical sides.
[0047] The cutting insert can comprise four identical corners and
four identical straight edges connecting the corners. It will be
understood that this provides a simple economic shape, free of
complex geometries. Stated differently, the insert can have a basic
square shaped edge with round corners. This shape can be the most
preferred shape which has long straight edges for cutting.
[0048] According to one preferred example each straight edge has an
edge length L.sub.E which fulfills the condition:
0.65I.sub.C<L.sub.E<0.95l.sub.C. Preferably, the edge length
L.sub.E fulfills the condition:
0.75I.sub.C<L.sub.E<0.90l.sub.C. Thus, for an extremely small
insert the entire straight edge on one side of the insert can serve
as a main cutting edge, and the entire straight edge on an adjacent
side can serve as a wiper. Notably, since the insert is so small,
the entire edge constitutes a relatively large wiper (raising the
concern above of wear when used as a wiper). In many known designs
this is overcome by a non-straight edge, i.e. a small wiper
adjacent to a corner followed by a relieved edge portion following
a different direction. In the present invention, however, each
straight edge can have a simpler geometry, serving as a larger
wiper when in one indexed position, and then functioning as a main
cutting edge after indexing of the insert. Notably, a large wiper
can provide better finish on a machined workpiece.
[0049] Alternatively, the basic insert shape can have a very small
straight edge and a very large corner radius for other than
90.degree. shoulder milling operations (resembling a circular
insert's operation). In such an embodiment, the edge length L.sub.E
fulfills the condition: 0.10I.sub.C<L.sub.E<0.50I.sub.C,
preferably 0.15I.sub.C<L.sub.E<0.35l.sub.C.
[0050] Still alternatively, the cutting edge can be, for example
circular.
[0051] Most preferably, the base bearing surface is ground. In a
most preferred embodiment, only the base bearing surface of the
cutting insert is ground. This is the most economical production of
the insert.
[0052] In some applications, it is necessary to carry out an
additional rake surface grinding operation. In such an embodiment,
the base bearing surface and the entire cutting edge are ground and
the cutting edge is contained within the square top. Stated
differently, the grinding operation is not conducted on the entire
peripheral surface, but merely along the top of the insert and
therefore the entire edge is contained within a plane, in this case
described as being contained within the square top. It will be
understood that such top grinding of the insert allows a multitude
of inserts to be ground in a single pass. While this is
disadvantageous in some respects, it can be offset by the pocket
being inclined to provide a suitable positive cutting position.
[0053] For some applications, it is also possible to produce a
cutting edge contained within the square top within desired
tolerances and without such a grinding operation, which is of
course preferred as it is more economical.
[0054] For greater stability, the abutment surface relief angle
.theta. preferably fulfills the condition
2.degree..ltoreq..theta..ltoreq.8.degree., and most preferably
4.degree..ltoreq..theta..ltoreq.7.degree..
[0055] In order to provide suitable performance, a cutting edge
land width W.sub.L measurable perpendicular to the insert axis
taken at any position along the cutting edge fulfills the
condition: W.sub.L.ltoreq.0.14 mm. Preferably the land width
W.sub.L fulfills the condition: 0.02 mm.ltoreq.W.sub.L.ltoreq.0.14
mm, or even more preferably 0.03 mm.ltoreq.W.sub.L.ltoreq.0.11 mm,
and most preferably 0.04 mm.ltoreq.W.sub.L.ltoreq.0.08 mm.
[0056] The pocket is preferably slanted with respect to the
rotation axis of the tool holder to compensate for a cutting edge
being planar, i.e. contained in the top square.
[0057] The pocket hole can similarly be comparatively large in
cross section compared with the distance to the lateral abutment
surfaces. This can be seen from a pocket hole diameter and
distances to the lateral surfaces.
[0058] The lateral surfaces are preferably typically oriented at
the same angle as the insert's abutment surfaces.
[0059] The screw axis can preferably be offset from the center of
the seat abutment surface, i.e., slightly more proximate to where
the lateral surfaces are closest to each other, so that a screw
holding the cutting insert to the pocket will bias the cutting
insert towards the lateral surfaces.
[0060] The most advantageous application for an insert in
accordance with the present invention is believed to be insert
mills for cutting small diameters, particularly for the standard
diameter ranges of 9.7 mm to 16 mm. Even though an insert mill of
the standard diameter size of 6 mm with a single cutting insert,
and insert mills of even larger diameters are possible, it is
believed that they are less efficient than other tool holders at
those sizes. For the small size insert exemplified (I.sub.C=4 mm),
insert mills at 9.7 mm diameter having two inserts, at 12 mm
diameter having two or even three inserts, at 14 mm diameter having
four inserts and at 16 mm diameter having five inserts are
feasible. It will be noted that the present invention is most
advantageous at the lower end of the diameter range mentioned,
particularly 9.7 mm and 12 mm insert mills. The benefit of which
can be noted by multiplying the number of inserts mentioned by four
(i.e. the number of indexable positions available for each
insert).
BRIEF DESCRIPTION OF THE DRAWINGS
[0061] For a better understanding of the subject matter of the
present invention, and to show how the same may be carried out in
practice, reference will now be made to the accompanying drawings
derived from a scale model, in which:
[0062] FIG. 1A is a side view of an insert mill comprising a tool
holder and a plurality of inserts according to the subject matter
of the present invention, rotated to show a front (i.e., axial)
view of the leftmost insert;
[0063] FIG. 1B is a side view of the insert mill in FIG. 1A,
rotated to show a side view of the leftmost insert in FIG. 1A;
[0064] FIG. 1C is an end view of the insert mill in FIGS. 1A and
1B;
[0065] FIG. 2 is an end view of an insert mill, similar to the
insert mill shown in FIGS. 1A to 1C, except with two inserts;
[0066] FIG. 3 is an end view of an insert mill, similar to the
insert mill shown in FIGS. 1A to 1C, except with five inserts;
[0067] FIG. 4 is a perspective view of the leftmost insert shown in
FIG. 1A;
[0068] FIG. 5A is a cross-section view taken along line VA-VA in
FIG. 6C;
[0069] FIG. 5B is a cross-section view taken along line VB-VB in
FIG. 6C;
[0070] FIG. 5C is a cross-section view taken along line VC-VC in
FIG. 6C;
[0071] FIG. 6A is a side view of the insert in FIG. 4;
[0072] FIG. 6B is a cross-section view taken along line VIB-VIB in
FIG. 6A;
[0073] FIG. 6C is a top (i.e. axial) view of the insert in FIG.
6A;
[0074] FIG. 7A is a top view of an imaginary square frustum,
showing the square top thereof;
[0075] FIG. 7B is a side view of the square frustum in FIG. 7A,
showing an isosceles trapezoid side surface thereof;
[0076] FIG. 7C is a bottom view of the square frustum in FIG. 7A,
showing the four isosceles trapezoid side surfaces thereof and the
square base thereof;
[0077] FIG. 7D is another side view of the square frustum in FIG.
7A, rotated;
[0078] FIG. 7E is a schematic side view of the insert in FIG. 4,
shown within the square frustum;
[0079] FIG. 7F is a perspective view of the square frustum in FIG.
7A;
[0080] FIG. 7G is a schematic perspective view of the insert in
FIG. 4, shown within a portion of the square frustum and hatching
schematically indicating where the trapezoid side surfaces of the
square frustum contain the side abutment surfaces of the cutting
insert;
[0081] FIG. 8A is a perspective view of a pocket of any one of the
insert mills in FIGS. 1A to 3;
[0082] FIG. 8B is a side view of the pocket in FIG. 8A;
[0083] FIG. 8C is a top (i.e. axial) view of the pocket in FIG. 8A,
and also constitutes a plan view of the seat abutment surface of
the pocket;
[0084] FIG. 9 is a perspective view of another insert and hatching
schematically indicating where the trapezoid side surfaces of a
square frustum (not shown) would contain the side abutment surfaces
of the cutting insert;
[0085] FIG. 10A is a cross-section view taken along line XA-XA in
FIG. 11C;
[0086] FIG. 10B is a cross-section view taken along line XB-XB in
FIG. 11C;
[0087] FIG. 11A is a side view of the insert in FIG. 9;
[0088] FIG. 11B is a cross-section view taken along line XIB-XIB in
FIG. 11A;
[0089] FIG. 11C is a top (i.e. axial) view of the insert in FIG.
11A;
[0090] FIG. 11D is a cross-section view taken along line XID-XID in
FIG. 11A;
[0091] FIG. 12 is a perspective view of another insert and hatching
schematically indicating where the trapezoid side surfaces of a
square frustum (not shown) would contain the side abutment surfaces
of the cutting insert;
[0092] FIG. 13A is a cross-section view taken along line
XIIIA-XIIIA in FIG. 14C;
[0093] FIG. 13B is a cross-section view taken along line
XIIIB-XIIIB in FIG. 14C;
[0094] FIG. 13C is a cross-section view taken along line
XIIIC-XIIIC in FIG. 14C;
[0095] FIG. 14A is a side view of the insert in FIG. 12;
[0096] FIG. 14B is a cross-section view taken along line XIVB-XIVB
in FIG. 11A;
[0097] FIG. 14C is a top (i.e. axial) view of the insert in FIG.
14A; and
[0098] FIG. 14D is a cross-section view taken along line XIVD-XIVD
in FIG. 14A.
DETAILED DESCRIPTION
[0099] FIGS. 1A to 1C illustrates an insert mill 10 configured for
90.degree. shoulder milling operations.
[0100] The insert mill 10 comprises a tool holder 12, cutting
inserts 14 and screws 16 for securing the cutting inserts 14 to the
tool holder 12.
[0101] The insert mill 10 is configured for rotating about a
rotation axis A.sub.R which extends longitudinally through the
center thereof.
[0102] The rotation axis A.sub.R defines opposite axially forward
and rearward directions D.sub.F, D.sub.R, and opposite rotational
cutting and non-cutting directions D.sub.C, D.sub.N.
[0103] The tool holder 12 comprises a shank portion 18 and a
cutting portion 20 extending forward therefrom.
[0104] The cutting portion 20 comprises one or more pockets 22.
[0105] In the example shown in FIGS. 1A-1C, there are three pockets
22 (shown without inserts in FIGS. 8A to 8C). For smaller diameter
tool holders it is only possible to provide less pockets, for
example a two pocket embodiment of an insert mill 10' is shown in
FIG. 2. For larger diameter tool holders more pockets may be
provided as shown in the tool holder 10'' in FIG. 3.
[0106] The cutting inserts 14, screws 16 and pockets 22, in the
examples given, are identical, therefore features described with
respect to one should be considered to apply to all.
[0107] The cutting insert 14 will now be described with reference
to FIGS. 4-6C.
[0108] The cutting insert 14 is a single-sided four-way indexable
cutting insert having a positive basic shape. It comprises a rake
surface 24, a generally planar base bearing surface 26, a
peripheral surface 28, a screw hole 30, and a cutting edge 32.
[0109] An insert axis A.sub.I (FIG. 6A) extends perpendicular to
the base bearing surface 26 and through the center of the insert
14. The insert axis A.sub.I is provided to assist defining
directions and features of the cutting insert 14. Generally
speaking, while it is most preferred that a screw hole of the
present invention is located in the center of an insert and is
perpendicular to a base bearing surface, resulting in an insert
axis of the insert also extending through the center the screw
hole, it will be understood that it is possible a screw hole can be
slanted or not perfectly central to a cutting insert, resulting in
a screw hole axis (not shown) which is not coaxial with the insert
axis A.sub.I (whereas in the present preferred example they are
coaxial). Nonetheless, given that the present invention seeks to
minimize material usage to the greatest extent possible, certainly
for the purposes of structural strength the exemplified central and
perpendicular screw hole is preferred.
[0110] The insert axis A.sub.I defines opposite upward and downward
directions D.sub.U, D.sub.D, and opposite inward and outward
directions D.sub.I, D.sub.O. The outward direction D.sub.O is not
meant to define one specific direction but rather all possible
360.degree. outward directions from the insert axis A.sub.I, three
such directions being exemplified. This is also true, in the
opposite direction, for the inward direction D.sub.I.
[0111] As shown, for example in FIGS. 4 and 5C, the rake surface 24
can preferably slope inwardly and downwardly from the cutting edge
to form an acute internal angle .alpha. for chip forming
purposes.
[0112] The base bearing surface 26 is generally planar as shown,
but it will be understood that this definition does not preclude
the possible inclusion of a small rounded transition edge between
the peripheral surface and the base bearing surface, as shown for
example in FIG. 7 of EP 3050655.
[0113] Referring to FIGS. 4 and 6A, the peripheral surface 28
comprises a lower sub-surface 34 and an upper sub-surface 36. The
lower sub-surface 34 is unground and extends upwardly and outwardly
from the base bearing surface 26, and comprises first, second,
third and fourth side abutment surfaces 38A, 38B, 38C, 38D. (In
FIG. 4 only 38A and 38B are shown and the positions of 38C and 38D,
which are hidden, are schematically identified; hereinafter the
identical side abutment surfaces will be identified generally as
"side abutment surface(s) 38").
[0114] Referring to FIGS. 6A and 6B, the positive basic shape of
the cutting insert 14 means that the lower sub-surface 34 forms an
obtuse internal angle .beta..sub.1 with the base bearing surface
26. Preferably, although optionally, the upper sub-surface 36 forms
an obtuse internal angle .beta..sub.1 with the base bearing surface
26. Alternatively, it is possible for the upper sub-surface 36 to
be, for example, perpendicular to the base bearing surface 26.
[0115] Each of the side abutment surfaces 38 is generally planar.
To elaborate, an exaggerated schematic convex bulge 40 is shown in
FIG. 6C. The bulge 40 typically results from a sintering process.
Since the inserts of the present invention are small, distortion
resulting in such bulge 40 is acceptably small enough for them not
to require grinding. Generally speaking, such convexity or
concavity (not shown; which can be considered an inward "bulge" for
the purposes of the specification) is measured as a maximum
distance from a plane connecting adjacent corners of an insert to
such bulge.
[0116] Thus, the insert is stated to have unground lower
sub-surface. Even though in FIG. 4, for example, it appears to have
a discontinuity line 42, this is merely a result of this particular
drawing showing a curvature line. An actual product which has not
been ground does not have a discernable line, and smoothly
transitions from the generally planar portion to the radius.
[0117] The upper sub-surface 36 comprises at least one overhanging
portion 44, described below further in reference to FIGS. 7A to
7G.
[0118] Referring to FIG. 6C, the cutting insert 14 can comprise
four identical corners 46A, 46B, 46C, 46D (hereinafter generally
referred to as "corner(s) 46") and four identical straight edges
48A, 48B, 48C, 48D (hereinafter generally referred to as "straight
edge(s) 48") connecting the corners.
[0119] Dimensions of various features are shown as follows: each
corner can have a radius R (FIG. 6C); each straight edge 48 can
have an edge length L.sub.E measured from the transition point of
the radius of the corners (FIG. 6C); a cutting edge land width
W.sub.L is shown in FIG. 5B; and an imaginary inscribed circle C,
and a diameter I.sub.C thereof is shown in FIG. 6C.
[0120] Referring to FIGS. 6B and 6C, a void volume V.sub.S of the
cutting insert 14 is defined by the boundaries of the screw hole
30. Specifically, a screw hole height H.sub.S is defined from the
base bearing surface 26 to an upper edge 49 of the screw hole 30
(also designated in FIG. 4). Stated differently, the void volume
V.sub.S is calculated as the volume of the void extending from a
bottom of the screw hole 30, defined at a lower plane P.sub.L
perpendicular to the insert axis A.sub.I and essentially coplanar
with the base bearing surface 26, to a top of the screw hole 30
defined at an upper plane P.sub.T perpendicular to the intersection
of the screw hole 30 and the rake surface 24, i.e. at the height of
the upper edge 49. More precisely, as shown in FIG. 5A, the upper
edge 49 is an intersection of a curved corner 51 of the screw hole
30 and the rake surface 24.
[0121] The material volume V.sub.F is, as its name states, the
volume of the actual material of which the cutting insert 14 is
made.
[0122] Referring now to FIGS. 7A to 7G, an imaginary square frustum
50 is shown comprising a square base 52, four identical isosceles
trapezoid side surfaces 54A, 54B, 54C, 54D (noting that in FIG. 7F
only 54A and 54B are shown and the positions of 54C and 54D, which
are hidden, are schematically identified; hereinafter generally
referred to as "trapezoid side surface(s) 54") and a square top 56
which is larger than the square base 52.
[0123] Each trapezoid side surface 54 extends upwardly and
outwardly from the square base at an abutment surface relief angle
.theta. (FIG. 7D) which is identical to the obtuse internal angle
.beta..sub.1 shown in FIG. 6B.
[0124] The hatching, schematically designated as 58A, 58B in FIG.
7G (noting that not the entire height of the square frustum is
shown) schematically shows where the first and second side abutment
surfaces 38A, 38B are respectively contained within the isosceles
trapezoid side surfaces.
[0125] Similarly, the square base 52 contains the base bearing
surface 26.
[0126] As, in this example, the cutting edge 32 is located at a
single height, i.e. a cutting insert height H.sub.I from the square
base 52, the square top 56 contains the cutting edge 32.
[0127] FIG. 7E shows, in a side view, where the at least one
overhanging portion 44 extends further outward from the isosceles
trapezoid side surfaces 54. In this example, there is only a single
overhanging portion 44, continuously extending around the entire
periphery of the insert.
[0128] The upper sub-surface 36 (FIG. 6A) begins, in the upward
direction, at a minimum upper sub-surface height H.sub.U above the
base bearing surface 26, the minimum upper sub-surface height
H.sub.U being measurable parallel to the insert axis A.sub.I. The
at least one overhanging portion 44 has a lowermost point 60 at the
minimum upper sub-surface height H.sub.U above the base bearing
surface 26.
[0129] Referring now to FIGS. 8A to 8C, the pocket 22 comprises a
seat abutment surface 62, a threaded pocket hole 64 opening out to
the seat abutment surface 62 and defining a minimal pocket hole
inscribed circle I.sub.P and an associated minimal pocket hole
diameter D.sub.P, first and second lateral abutment surfaces 66A,
66B oriented at a right angle to each other in a plan view (i.e.
the view in FIG. 8C) of the seat abutment surface 62.
[0130] The pocket hole 64 can similarly be comparatively large in
cross section compared with the distance to the lateral abutment
surfaces. This can be seen from the pocket hole diameter D.sub.P
and the distances from the pocket hole 64 to the lateral abutment
surfaces 66A, 66B.
[0131] The first and second lateral surfaces 66A, 66B are
preferably typically oriented at the same obtuse internal angle
.beta..sub.1 as the insert's abutment surfaces 38.
[0132] A screw axis A.sub.S can preferably be offset from a center
of the seat abutment surface, i.e. slightly more proximate to where
the lateral surfaces are closest to each other (i.e. the area
generally designated 68) so that a screw holding the cutting insert
to the pocket will bias the cutting insert towards the lateral
surfaces.
[0133] Referring now to FIGS. 1A to 1C, a tool recess 70 is
preferably provided so that a tool can easily access a screw 16
mounted to the pocket 22.
[0134] When mounted, the screw 16 secures the cutting insert 14
such that the base bearing surface 26 abuts the seat abutment
surface 62, the first abutment surface 38A abuts the first lateral
surface 66A, and an adjacent abutment surface 66 (in this example
the fourth abutment surface 38D, shown in FIG. 1C) abuts the second
lateral surface 66B. It will be understood that the cutting insert
14 can be indexed four times in the pocket 22 and that the exact
designation of which specific abutment surfaces contact at any
given time is not important.
[0135] More importantly, it is noted that the upper sub-surface 36
does not contact the tool holder 12 and therefore inserts with
different cutting edges can be mounted on the same tool holder
12.
[0136] The pocket is preferably slanted in the forward direction
D.sub.F and cutting direction D.sub.C with respect to the rotation
axis A.sub.R, as shown by a slant angle .mu.. The slant angle .mu.
can preferably fulfill the condition
2.degree..ltoreq..mu..ltoreq.5.degree..
[0137] In FIG. 1B, for the insert mill 10 exemplified, one of the
straight cutting edges (for example the third straight edge 48C)
performs a wiper function and only protrudes a small wiper distance
D.sub.W from the tool holder. Notably the orientation thereof is at
a right angle to the rotation axis A.sub.R. In this example, the
second straight edge 48B is the main cutting edge for providing a
90.degree. shoulder milling operation.
[0138] Referring to FIG. 1A, since the entire cutting edge 48
(exemplified as the second straight edge 48B) is straight and
generally parallel to the rotation axis A.sub.R, a comparatively
large cut depth A.sub.P is achievable for a comparatively very
small cutting insert. For the same reason, this is similarly true
that the entire third straight edge 48C provides a comparatively
large wiper, generally perpendicular to the rotation axis
A.sub.R.
[0139] Referring now to FIGS. 9 to 11D, a different insert
embodiment, i.e., a circular insert 14', is shown. The pocket's
first and second lateral abutment surfaces 66A, 66B have no gap in
the center thereof, as is typically provided to counter an insert
bulge described above. Because the pocket's first and second
lateral abutment surfaces 66A, 66B are devoid of a gap, a circular
insert such as the cutting insert designated 14', which will abut
the center portions of the first and second lateral abutment
surfaces 66A, 66B can be used in the exact same pocket 22 as the
previously described insert 14.
[0140] The circular insert 14' is a single-sided four-way indexable
cutting insert having a positive basic shape. Apart from the shapes
of the cutting edge 32', side abutment surfaces 38' and overhanging
portions 54', the circular insert 14' can be considered to be
otherwise similar to the previously described insert 14.
Accordingly, only significant differences will be detailed.
[0141] Reference numerals corresponding to those used in the
previously described insert, but suffixed with an apostrophe (')
should be considered to have comparative function.
[0142] The cutting edge 32' is completely circular and hence also
corresponds to the imaginary inscribed circle C'.
[0143] The side abutment surfaces 38' can preferably but optionally
taper in the downward direction D.sub.D (FIG. 11A). Stated
differently, they can have a frustum shape (noting that it is not a
triangular shape since the overhanging portion is not included as
part of the side abutment surface).
[0144] While the tapering shape extends from the cutting edge 32'
to the base bearing surface 26', it will be understood that the
abutment of the side abutment surfaces 38' and the pocket's lateral
abutment surfaces will only be with the hatched portions, two of
which are shown in FIG. 9.
[0145] Finally, it will be noted that at least one overhanging
portion 44' is actually four spaced-apart, separate overhanging
portions. As shown in FIG. 10B, in contrast to FIG. 10A, certain
circumferential portions of the peripheral surface 28' are devoid
of any overhanging portion 44'. FIG. 10A is view through a cross
section through the center of the side abutment surface 38' as
understood from FIGS. 11C and 11D. By having a plurality of
spaced-apart overhanging portions, both a fully circular cutting
edge can be achieved while still having four generally planar side
abutment surfaces vertically separated from the cutting edge for
providing four distinct indexing positions.
[0146] Referring now to FIGS. 12 to 14D, a different insert
embodiment, i.e. a feed insert 14'', is shown.
[0147] The feed insert 14'' is similar to the previous inserts in
most respects except that the cutting edge has been designed for
feed milling (i.e. comprising combined ramping and feed machining
capability. Accordingly, only significant differences will be
detailed.
[0148] Reference numerals corresponding to those used in the
previously described insert, but suffixed with two apostrophes ('')
should be considered to have comparative function.
[0149] The feed insert 14'' merely exemplifies that the side
abutment surfaces 38'' can be located in a position other than the
center of the side surface of the insert. Stated differently, they
can be generally planar only adjacent to corners of the insert. The
hatched portions of the side abutment surfaces 38'' in FIG. 12 will
similarly be contained within the above described isosceles
trapezoid side surfaces. Thus the same tool holder 12 can also be
used to provide a feed function.
* * * * *